The present invention generally relates to the field of vented battery caps, and more particularly, to the field of multiple plug vented battery caps which are designed to arrest the ignition and/or to minimize the explosive potential of battery gases upon their expulsion into the atmosphere. It is well known that a suitable battery vent plug must provide for the expulsion of gases which are built up during the chemical charging and discharging action of the battery, while effectively preventing the leakage or evaporation of substantial quantities of battery electrolyte. To this end, battery vent plugs are normally designed with gaseous connection means for venting the gases produced within the battery to the atmosphere, while providing electrolyte retention means within the battery vent plug for retaining and returning as much of the electrolyte to the battery as is practically feasible. This retention of battery electrolyte is normally accomplished through the use of various baffles and/or gabled floors of the battery vent plug which tend to funnel the battery electrolyte which escapes into the battery vent plug back into the battery cells.
Originally, few provisions were made apart from those described above in order to minimize the chance that a spark in the vicinity of the battery would ignite the battery gases, thereby resulting in the possible explosion of the battery vent plug away from the battery container and/or the explosion of the battery itself. More recently, attention has been focused upon the desirability of minimizing the chance that a spark in the vicinity of an operating battery would indeed ignite those gases upon their expulsion to the atmosphere and, alternatively, have attempted to insure that the inadvertent ignition of those gases would not have explosive results. One approach to solving this problem has been to provide a multiple battery vent plug in which gaseous communication was provided from the center of each plug through the body of the plug to four rectangularly widely spaced apart pin hole-like gas outlets disposed on the top cover of the battery for venting these explosive battery gases to the atmosphere, presumably in a diffuse manner. Alternatively, in single battery vent plugs, the interior of the plug which is directly in communication with the battery cell communicates with a gaseous passage disposed under the top surface of the plug by a slot, having a longitudinal member disposed therein, presumably to prevent battery electrolyte from entering the gaseous passage. Two pin hole-like openings are spaced apart on the upper surface of the rather broad cap, again for the purpose of diffusing the explosive battery gases into the atmosphere.
Other designs for venting battery gases safely into the atmosphere have tended to replace pin hole-like openings with larger cylindrical or rectangular openings in which or next to which is disposed a porous ceramic diffuser. These ceramic diffusers are particularly adapted for use in multiple battery vent plugs having a hollow body which is adapted for the mounting of such a porous diffuser in a position intermediate between two adjacent battery plugs. One such porous diffuser for a single battery vent plug is disclosed in French Pat. No. 839,808 (1939). Alternatively, another type of microporous membrane is disclosed in U.S. Pat. No. 3,507,708. U.S. Pat. No. 3,879,227 discloses such a porous diffuser disposed within a multiple battery vent plug. As with most battery vent plugs, the battery vent plugs described in the above mentioned patents are normally provided with sloping surfaces and/or baffles to prevent or inhibit battery electrolyte from contacting the porous diffuser and/or other vent means.
In particular, in addition to having a porous diffuser located adjacent to the atmosphere, U.S. Pat. No. 3,879,227 discloses a compartment disposed between the porous diffuser and the atmosphere, which compartment has an elongated outlet opening to the atmosphere, the ratio of the volume in cubic inches of the compartment to the area of the elongated outlet in square inches being within a particular range. Presumably, this configuration minimizes the effect of explosions which occur in the area immediately adjacent to the porous diffuser, and the size of the compartment and cross sectional area of the elongated opening are so selected as to prevent explosions occurring within the compartment from having serious consequences. To this end, the exterior surface of the compartment is so constructed so that upon the ignition of gases within the compartment the elongated opening has a tendency to increase in cross sectional area, thereby venting the ignited gases directly into the atmosphere. Other patents which generally show multiple battery vent plugs include U.S. Pat. Nos. 3,284,244, 3,265,538, 3,369,940 and 3,597,280. Other battery vent patents include U.S. Pat. Nos. 3,466,199, 2,670,396 and the references cited thereon.